Epidemiologic data demonstrate an inverse relationship between circulating levels of high density lipoprotein cholesterol (HDL-C) and the incidence of clinically significant atherosclerosis. Each 1 mg/dl increment in the HDL-C serum level is associated with a 2-3% decrement in cardiovascular risk; a 1% reduction in LDL-C reduces coronary heart disease (CHD) risk by 2%. Gordon et al., Am. J. Med. 62(5):707-14 (1997). Experimental evidence further supports the protective effect of HDL against cardiovascular disease. For example, in subjects with low HDL-C, administration of gemfibrozil results in a 6% increase in the HDL-C level and a corresponding 22% reduction of the CHD risk. Rubins et al., N. Engl. J. Med. 341(6):410-8 (1999). Observations in genetic disorders associated with low HDL due to reduced ApoA-I expression, also indicate the link between elevated risk of CHD and low HDL-C.
HDL appears to exert its antiatherogenic effect by mediating reverse cholesterol transport (RCT), in which cholesterol is recruited from peripheral tissues and transported to the liver. In addition, HDL also exerts anti-inflammatory, antioxidant effects and promotes fibrinolysis. HDL particles protect against oxidation of LDL, an important initial step in promoting cholesterol uptake by arterial macrophages. HDL exists in two main forms, one containing both apolipoprotein A-I (ApoA-I) and apolipoprotein A-II (ApoA-II), and the other containing ApoA-I without ApoA-II. Schultz et al., Nature 365(6448):762-4 (1993). The cardioprotective effect of HDL is mostly, but not exclusively, attributable to ApoA-I.
Clinical and experimental data suggest that the production of ApoA-I is a critical determinant of circulating HDL. For example, persons with familial hyperalphalipoproteinemia (elevated ApoA-I) appear to be protected from atherosclerosis, while those deficient in ApoA-I (hypoalphalipoproteinemia) show accelerated cardiovascular disease. In addition, various experimental manipulations to increase production of ApoA-I are associated with reduced atherogenicity. For example, human ApoA-I is protective in transgenic animal models (Shah et al., Circulation 97(8):780-5 (1998; Rubin et al., Nature 353(6341):265-7 (1991), and treatment with ApoA-IMilano prevents atherosclerotic lesions and leads to regression of atherosclerotic plaques in human patients (Nissen et al., JAMA 290(17):2292-300 (2003)). Further lines of research supporting an antiatherogenic role of ApoA-I include enhancement of reverse cholesterol transport, attenuation of oxidative stress, increased peroxonase activity, enhanced anticoagulant activity, and anti-inflammatory activity. Accordingly, ApoA-I is an attractive target for therapeutic intervention.
Currently available therapeutic agents that increase the plasma concentration of ApoA-I, for example, recombinant ApoA-I or peptides that mimic ApoA-I, have potential drawbacks related to manufacturing and reproducibility, e.g., stability during storage, delivery of an active product, and in vivo half-life. Therefore, small molecule compounds that upregulate the production of endogenous ApoA-I, such as, e.g., transcriptional upregulators of ApoA-I expression, are very attractive as new therapeutic agents for cardiovascular disease.
One class of compounds that are thought to contribute to the prevention of various diseases, including cancer and cardiovascular diseases, is polyphenols. Polyphenols are common constituents of the human diet, present in most food and beverages of plant origin, and are the most abundant dietary antioxidants. However, polyphenols protective properties are often minimized due to poor bioavailability, lack of clinical significance, and deleterious effects at high concentrations. For example, the most abundant and available source of resveratrol for consumers, red wine, cannot be consumed in therapeutically efficacious quantities on a daily basis due to the numerous well documented deleterious effects of excessive alcohol consumption. The actions of resveratrol may be better or safer in the absence of alcohol.
Several human clinical studies, involving foods or beverages, have yet to demonstrate an unequivocal benefit on primary clinical endpoints, such as oxidative stress, lipemia, and inflammation. For example, out of 12 recent intervention studies with differing polyphenol sources, 6 showed no effect on lipid parameters and the other 6 showed an improvement in the lipid parameters. Manach, Curr. Opin. Lipidol. 16(1):77-84 (2005). Such contradictory data has limited the potential use of polyphenols, despite their many beneficial properties.
The use of naturally occurring polyphenols as a potential therapy has also been impeded by the inability to achieve efficacious levels of bioavailability. The bioavailability of polyphenols in humans range from 1% to 26% and has a large inter-individual variability as well as variability between different polyphenols. Polyphenols differ in how they are absorbed, metabolized, and excreted. For example, polyphenol flavonoids, such as quercetin, have been reported to have less than 1% intestinal absorption following oral administration. Gugler et al., Eur. J. Clin. Pharm. 9:223 (1975). In addition, metabolites are known to negatively influence the biological activity of the parent compounds. Such metabolites often differ from the parent compound in terms of toxicity, efficacy, and length of residence in the plasma. Another limiting factor may be polyphenols' poor solubility in water which limits the routes of administration. These and other factors have made it difficult to determine appropriate dosages of the naturally occurring polyphenols, naringenin or resveratrol, for use in humans.
Thus, there exists a need for synthetic polyphenols to be developed as therapeutic agents for the treatment and prevention of cardiovascular and related diseases, particularly, cholesterol or lipid related disorders, such as, e.g., atherosclerosis. It is therefore one of the objects of the present invention to provide compounds that upregulate the expression of ApoA-I, while having more favorable pharmacological properties than naturally occurring polyphenols.